Sagehen Creek Field Station

23 Aug, 03 AM - 27 Aug, 11 AM

The purpose of the project is to develop reliable quantitative estimates of the amount of additional groundwater storage that can be provided in the Sierra Nevada as a result of geomorphic restoration of wet meadows on national forest system lands Task: Field check meadow delineations Meadows will be considered to be all valley-bottom alluvial landforms with topographic slopes less than 8% and underlain by fine-grained alluvial and organic strata. Vegetation will not be used as a criterion, to allow the inclusion of former meadows that have been converted to xeric vegetation as a result of erosion. Polygons delineated as meadows that are found on inspection to not meet these criteria will be replaced by additional random selections from the population of delineated meadows. Meadow locations and areas will be determined by recording points along the meadow perimeter with a GPS unit using NAD83 coordinates. Perimeter points will be used to create polygons to update the GIS meadow delineation coverage. The locations and areas determined in the field will be compared to the original delineations based on topographic slope to estimate the overall accuracy of the slope-based delineations. Task: Determine extent of erosion in selected meadows After delineation of meadow perimeters, the selected meadows will be classified as either eroded or non-eroded. Given the variability in meadow conditions, absolute quantitative criteria for classification are difficult to establish, and professional judgment on the part of the field survey crews will be required. USFS watershed specialists will work with partners to ensure consistency among field surveys. As general guidelines, meadows will be classified as eroded if the following conditions are observed: * Near-vertical unvegetated channel banks with heights of 2 feet or more over 25% or more of total channel length through the meadow * Knickpoints or headcuts greater than 2 feet in height * Bank heights decreasing downstream * Channel bed elevations more than 1 foot below the rooting depths of riparian plants * No evidence of recent overbank flows on the meadow surface. Meadows will not be classified as eroded or non-eroded based solely on historic or current land uses. Physical evidence of erosion must be present for meadows to be classified as eroded. Average gully depths will be measured at 10 locations at approximately equal intervals along the channel thalwegs of eroded meadows. Gully depths will be measured as the vertical distances between thalweg and meadow surface elevations along gully banks using hand levels and surveying rods. Average depths will include observations of zero depth for locations on eroded meadows that are not incised by gullies. However, no channel depth measurements will be made on meadows classified as non-eroded. In order to better understand the causes of meadow erosion and the potential for future erosion of meadows that are currently geomorphically stable and hydrologically functional, the topographic slope of each meadow and its upstream drainage area will be determined from GIS analysis of the DEM (see for example Wood, 1975). Meadow slopes will be field checked using clinometers during field surveys. Synthesis * Total number and area of meadows, including meadows dewatered due to erosion, on national forests in the Sierra Nevada, based on topographic delineations of meadows and subsequent field checks * Proportion of these meadows that are eroded by gullies, based on field assessment of 100 randomly selected meadows * The significance of the relation between meadow slope and upstream drainage area for meadow stability (for example, Wood, 1975) * Estimated total volume of meadow alluvial groundwater storage capacity that could be provided by complete restoration of eroded meadows on national forests in the Sierra Nevada, based on field measurements of meadow areas and gully depths and laboratory measurements of specific yield of meadow alluvium (the ?sponge? function) * An estimated range of hillslope-bedrock groundwater storage attributable to flow restriction by low-permeability meadow strata, based on short-term late summer water budgets for 12 meadows (3 in each of 4 geologic units; the ?valve? function) * Estimated total combined groundwater storage, both within meadows (the ?sponge? function) and hillslope-bedrock systems (the ?valve? function), potentially achievable through meadow restoration on national forests in the Sierra Nevada.

Visit #22738 @Sagehen Creek Field Station

Approved

Under Project # 22341 | Research

Sierra Nevada Meadows Hydrologic Assessment

research_assistant - University of California, Davis

Reservation Members(s)

Group of 2 Research Assistant (non-student/faculty/postdoc) Aug 23 - 27, 2010 (5 days)
Jennifer Hemmert Aug 23 - 27, 2010 (5 days)

Reserve Resources(s) | Create Invoice

East Cabin (Lower Camp) 3 Aug 23 - 27, 2010